With more testing I found that the context menu position depends (perhaps solely) on whether my mouse pointer is on the left side or the right side of the horizontal half of the rightmost monitor: if you imagine a vertical line dividing the rightmost monitor’s display area into two equal-sized halves, right-clicking anywhere on the left side of that line brings up the menu on the correct display, whereas right-clicking anywhere on the right side brings it up on the wrong display.

(That is why I first made the mistake of thinking links weren’t affected: the ones I tried first just happened to be on the left side.)

Unfortunately I don’t have a third display to verify that I’m really seeing a different manifestation of the same bug as Nathaniel, of one that depends on the monitor count.